Police in India's capital, Delhi, have released sketches of a man they want to question in connection with Saturday's explosions that killed 62 people.
The sketches were developed by talking to eyewitnesses
They say the man is in his early 20s and was seen leaving a bag on a bus. The bag exploded soon after he got off.
An alert bus driver was throwing the bag out as it detonated, injuring himself but preventing any deaths.
It remains unclear who carried out the raids. India has hinted at a Pakistani link - a claim rejected by Islamabad.
Observers say India has been careful not to blame publicly any particular group, as the two countries make tentative progress in their peace process.
Delhi police released three sketches of the man they suspect of planting the bomb in the bus in the Govindpuri area of Delhi.
The three sketches show him separately clean-shaven, with a moustache and with a goatee beard - apparently in case he tries to change his appearance.
He is also said to have a bandage around his head and a bandaged left arm.
A police official told the BBC that the sketch had been developed by talking to witnesses and those on the bus.
The driver, Kuldeep Singh, remains in hospital where he is receiving treatment for his injuries. The conductor and several others were also hurt.
"Both men are national heroes," A Majumdar, chairman of Delhi Transport Commission which employs them, told Reuters.
"Dozens would have died if he and the conductor had
not acted in time."
Several people have been questioned over the attacks including witnesses at the three blast sites in Paharganj, Sarojini Nagar and Govindpuri.
The attacks came ahead of the Hindu festival of lights, Diwali, and Muslim celebrations for Eid, marking the end of the holy month of Ramadan.
DELHI BOMB SITES
Paharganj: 16 die near train station at 1745 (1315 GMT)
Sarojini Nagar: 43 killed, minutes after Paharganj attack
Govindpuri: Bus driver throws bomb from vehicle - no deaths
Figures from Sunday
Diwali celebrations on Tuesday were uncharacteristically subdued in Delhi.
People entering markets and temples were subjected to heavy security checks and armed police were deployed across the city.
More than 200 people were injured in the attacks, of whom about 90 remain in hospital, some in a critical condition.
On Monday, India gave its clearest indication yet as to who it thought was behind the bombings, when the prime minister hinted that Pakistan-based militants were involved.
Mr Singh told Pakistani President Pervez Musharraf he was "disturbed and dismayed at indications of the external linkages of terrorist groups with the 29 October bombing".
Islamabad, which was swift to condemn the bombings and offer support, says it has no indication that Pakistani groups were involved.
On Tuesday, leading Pakistan-based Islamic militant group Lashkar-e-Toiba denied it had anything to do with the blasts.
Its name has featured widely in speculation about who might be responsible and it has frequently been accused by India of attacks in the past.
A little-known Kashmiri group said on Sunday it had been behind the attacks. Police say they are trying to verify the claim by Islami Inqilabi Mahaz.